To spectators, the 10-hour lift of a 528-ft-wide, 2,650-ton steel-truss-span assembly that is part of the Huey P. Long Bridge widening project may have seemed like watching paint dry, says John Brestin, project manager for consulting engineer HNTB Corp., Kansas City. “But when you think about the fact this was three years in planning—from concept to design to getting it up—it was more like the blink of an eye.”

And after the successful June 19 lift, HNTB and the contractor, MTI, say they expect subsequent lifts will be several hours faster when the next span, over the Mississippi River’s main navigation channel, is lifted into place in November.

The entire bridge widening project is valued at $1.2 billion.

For the first lift, road, rail and river closures were needed from Friday morning, June 18, through the following Monday, as the span was barge-positioned beneath the bridge, lifted, slid laterally into place and attached. Then its stabilizing frame was disconnected, lowered back onto the barges and returned to shore.

Contractor MTI—a joint venture of Massman Construction Co., Kansas City, Mo., Traylor Bros. Inc., Evansville, Ind., and IHI Inc., New York City—hired HNTB to devise the span-by-span sequence on the $452.6-million, phase-three superstructure erection of the fourphased bridge widening. The pre-assemble-and-lift scheme was deemed safer than stick-building, for both the bridge and contractor, and it was less disruptive to navigation, says Steve Underwood, MTI project manager.

Expanding the deck width by building around the existing bridge requires simultaneously lifting two separate halves of the truss, rather than hoisting a complete assembly, which is “pretty amazing—probably one of the most unique jobs going on now in the world,” says Massman’s president and CEO, Henry Massman.

Hans Hutton, HNTB’s senior engineer, designed two U-shaped stability frames to support the truss halves and hold them plumb during erection, Brestin says. The 6-ft-deep, 160-ft-long box-section floor beams of the 850-ton stability frames connect the trusses on either side from underneath. MTI installed pre-fabricated, 22-ft x 22-ft x 30-ft-tall lifting towers topped by sliding cantilevered beams on the bridge piers at either end of the existing span to support the four 900-ton strand jacks that vertically lifted the new span 130 ft.

MTI devised a four-barge assembly platform, connected by three sectional barges, on which to erect the stability frames and build the new truss. Construction began on April 23 and was finished on May 31, says Clair Stewart, an MTI project engineer. Constructing the truss on the connected barges required engineering a system of sliding tracks and counterweights, Stewart says. The counterweights run up and down each barge to adjust ballast while the truss was built.

The new truss was barged into place beneath the receiving span on June 18. River traffic in the secondary channel running through the worksite was shut down for the weekend and into Monday.

In addition, to avoid large ship wakes while tugs were positioning the barges beneath the bridge, the main navigation channel also was closed from 9 a.m. to 5 p.m. on Friday and closed again for four hours, starting at 5 a.m. on Saturday at the beginning of the critical liftoff sequence. Ensuring stability during the tight liftoff window took more than two hours longer than expected.

“We had lift-off from the barge at 6:30 a.m., but then it took two to three hours of preparation to stabilize it,” Brestin says. The liftoff and the lateral, 13-ft move to seat the truss-halves on their bearings were the two most critical times in the placement, Brestin says.

In early 2008, CTL Group, Skokie, Ill., installed a monitoring system on eye bars and truss members of the bridge so HNTB could establish a baseline of ambient stresses and determine allowable tolerances for axial and bending stresses during construction.

To monitor the new truss for out-of-plane distortions while it was being moved, lifted and installed, Applied Geomechanics Inc., San Francisco, installed a system of tilt meters and laser-deflection devices on the truss that delivered real-time graphic displays of how the steel was responding, says Thomas Weinmann, manager of AGI’s structural health monitoring group.

Following the unexpected, two- to three-hour stabilization period at lift-off and the 10-hour lift, the final process to slide the truss halves 13 ft toward each other and onto the bearings, lasted from 4 p.m. to midnight, Brestin says. MTI used eight 50-ton and four 100-ton cylinder jacks to laterally move the truss, meaning six jacks had to move in unison on each side. “When we hooked up to the existing bridge, we had a train go by once we captured a bottom chord,” Brestin says. “The impact really shook the trusses and caused the top to move a little bit.” Traffic on the two rails was halted until the lateral move was complete.

“The lateral move was the most critical point, when there was the most potential to move the truss out of plane,” Brestin says. “We had six jacks moving in tandem, and if one got far ahead of another, it could cause buckling.”

The bottom chord of the new truss was positioned on the existing bridge with four pins set into the top of the bearings and then secured with bolts, Underwood says. Using a ringer crane positioned on a barge on the upstream side and another crane on the deck of the bridge on the downstream side, MTI placed four hornbeams to straddle and secure the top chords. Once the new truss was secured by those and additional struts, the stability frame was disconnected, lowered onto the barges and moved to shore where the next span will be assembled. Then MTI set to work installing secondary members.

Robert Kollmar, chief engineering officer of New Orleans Public Belt Railroad, which owns the bridge, is “thrilled” that MTI chose to construct using the span-by-span method. “I expect that any delay to freight train and impact to operations will be minimal, and it produces less stress on the bridge,” he explains.

David Frank, bridge administration chief for the U.S. Coast Guard district, says the span-by-span lift is “a phenomenal improvement for navigation” over the obstructions caused by falsework in the river for stick-built construction. “The design is less invasive and has been a phenomenal melding of industry, public-private partnering, contractors and the federal government,” Frank says. “If MTI had stick-built, we would have had to close the waterway for a significantly longer amount of time and had greater risk.” MTI performed within the scheduled closure times and even faster on two occasions, Frank says.

“I have yet to have a complaint from either shallow- or deep-draft people regarding the construction,” Frank adds.

Brestin says the lessons learned from this lift will allow MTI to deliver faster when the main navigation span is placed in November 2010 and the final span is placed in May 2011. “I think the big portions of the plan went exactly as expected,” Brestin says. “Some of the smaller things—blocking between the truss and the floor beam, our monitoring system as we went up and capturing the existing bottom chord—we’ve learned how to do faster for the next time.”